Disc drives typically use magneto-resistive read heads to support high data densities. These magneto-resistive heads require a DC bias to operate (typically provided by a preamplifier). In a mobile application, however, power consumption is an important issue. Thus, a number of techniques have been proposed or suggested to reduce the power consumption of disc drives for mobile applications. Biasing of magneto resistive heads is also varied over time to extend the lifetime of the sensor. For example, sample and hold circuits have been proposed to allow the bias control circuits of the read head to be powered down when writing data to the disc while maintaining short write-to-read transition times.
In one proposed implementation of a sample and hold circuit, the disc drive power consumption was effectively reduced, but the maximum hold time was only on the order of 30 microseconds, due to switch leakage paths. For a number of applications, however, a longer hold time may be necessary.
Data acquisition systems typically monitor and quantize analog signals to allow digital techniques to be used for signal analysis and data storage. To minimize costs, a multiplexer is usually placed between the signal sources and an analog-to-digital converter (ADC). For precision data measurement, it is important to minimize the effects caused by the input signals associated with the unselected inputs being coupled into the selected signal path. Current methods of implementing the multiplexer in CMOS technology suffer from finite switch leakage resistance and from parasitic diode leakage from the MOS device into its isolation diffusions.
A need therefore exists for a disc drive having a sample and hold technique with a longer hold time. A further need exists for a disc drive employing a sample and hold technique that provides improved read-to-write and write-to-read mode transitions. A need also exists for circuits and techniques to minimize the effects of switch leakage resistance and leakage through the drain and source junction diodes into the isolation diffusions of switches in an analog multiplexer.